The present invention relates to a method for pressing a material so that the material is fed into a gap formed by two pressing surfaces, in which gap the cross section of the material flow is tapered in the direction of the flow, and the material is compacted and pressed between pressing surfaces formed of parallel, beam-shaped transfer elements, which are reciprocatingly moved in the direction of the material flow so that the mutually opposed transfer elements of both pressing surfaces are moved in a mutually synchronized manner in the same direction and so that during the forward transfer motion the pressing force exerted by the transfer elements on the material is greater than the pressing force exerted during the return motion of the transfer elements. Furthermore, the invention concerns a press for compacting and pressing a material, said press comprising two opposed pressing surfaces whose mutual distance tapers in the direction of the material flow and which are formed by parallel, beam-shaped transfer elements provided with means for moving the elements in a reciprocating manner in the direction of the material flow so that the opposed transfer elements of both pressing surfaces are moved in a mutually synchronized manner in the same direction and so that during the forward transfer motion the pressing force exerted by the transfer elements on the material can be relaxed during the return motion.
Different types of presses are conventionally used for, e.g., dewatering bark resulting from debarking of wood in order to improve its solids content. The bark is used for firing, but prior to such a use, it must be dewatered. Dewatering has been accomplished by means of ram and roll presses of different types. Various constructions of presses have been described in, e.g., the Finnish patent publication 78020. A problem of conventional roll press implementations has arisen, i.a., from the feed of bark into the narrow nip of the press. The actual pressing time remains relatively short in roll presses, and consequently, it has been necessary to recirculate the bark several times through the pressing nip. Since the compressed bark, however, has a chance of decompressing between the nips, a part of the expelled water can re-enter the bark. Other problems have also been caused from the fact that the pressing surfaces perforated for the passage of expelled water must take extremely high backing forces. Discharge of water has generally been possible via only one of the surfaces, namely the lower pressing surface supporting the bark flow.
Transferring and pressing presses constructed from parallel, beam-shaped transfer elements are known from U.S. Pat. Nos. 2,271,599, 2,340,607 and 2,278,552, G. Maurer, and 3,850,213, D. Keaton, and 2,107,607, K. Gobel. These presses are not, however, designed for compacting and pressing a material of extremely high fluidity or liquid content. The presses disclosed in the foregoing patents are closest suited to pressing and transferring board-like products.